# Corrected QT Interval (QTc) Calculator

The QT interval represents the duration of ventricular electrical systole, it is measured from the beginning of the QRS complex to the end of the T wave.

The QT interval varies depending on heart rate, it decreases at faster heart rates and it lengthens at slower heart rates, so it should undergo adequate rate correction (corrected QT or QTc).

To calculate the corrected QT interval (QTc) you need the QT interval duration and heart rate of the EKG.

Related article: Hydroxychloroquine on the EKG.

## Corrected QT Interval (QTc)

### QT interval duration

QT interval duration in ms:

ms

Click if you prefer to enter the number of small squares.

Number of small squares:

squares

Click if you prefer to enter the QT interval duration in ms.

### Heart rate

Heart rate:

bpm

Click if you prefer to enter the R-R interval.

R-R interval:

ms

Click if you prefer to enter the heart rate.

• Long QTc: greater than 460  ms in children under the age of 15, 450 ms in men, and 470 ms in women 1.
• Short QTc interval: less than 340 ms is accepted as pathological.

We use Framingham corrections 2 in this calculator because it has more uniform correction over a wide range of heart rate 3.

Remember, this calculator is not 100% reliable, and it is not a substitute for traditional methods of corrected QT interval calculation, nor electrocardiogram evaluation made by a doctor or competent professional.

## How to use the corrected QT Calculator

To enter the value of the QT Interval, you can either directly enter its duration in milliseconds or, if you wish, enter the number of small squares it comprises.

Remember that the QT interval is measured from the beginning of the QRS complex to the end of the T wave.

Enter also the value of the heart rate to make the correction, you also have the option to enter the length of the R-R interval if you wish.

Example: calculate QT interval, from the beginning of the QRS complex to the end of the T wave.

#### References

• 1. Johnson JN, Ackerman MJ. QTc: how long is too long? Br J Sports Med. 2009 Sep; 43(9): 657–662. doi: 10.1136/bjsm.2008.054734.
• 2. Sagie A, Larson MG, Goldberg RJ et al. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol. 1992;70:797–801. doi: 10.1016/0002-9149(92)90562-d.
• 3. Vandenberk B, Vandael E. Which QT Correction Formulae to Use for QT Monitoring? JAHA 2016;5:e003264. doi: 10.1161/JAHA.116.003264.

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